In the production of cheese, curd, and milk protein powders, a process stage of essential importance is the separation of the main components of milk from each other, i.e. the separation of fat and protein--or in fatless products the separation of protein only--from lactose. Traditionally, this has been carried out by precipitating casein or a mixture of casein and fat by means of a rennet enzyme or by adjusting the pH by means of an acid to the isoelectric point (pH about 4.5). Whey proteins as well as lactose and salts normally remain in the solution, i.e. the whey.
Consequently, several processes have been developed for improving the protein yield. By the use of heat treatment or calcium addition, the whey proteins are caused to precipitate with casein. Besides lactose and salts, only low molecular weight nitrogenous compounds remain in the solution part. The utilization of this kind of proteinless whey is very difficult.
New processes have been developed besides the precipitation processes. In the early 1970's, the gel filtration was believed to offer a satisfactory technical solution to the recovery of milk proteins in a soluble form (U.S. Pat. No. 3,547,900). In the gel filtration, the protein fraction of milk is separated from the lactose and the salt of milk. However, the industrial applications of the process have been prevented by the high price and difficulties in the treatment of the gel material as well as hygiene problems.
The ultrafiltration, process also developed in the 1970's, and has been applied industrially especially in the production of Feta cheese, curd, and a whey protein powder. The most important reason why the ultrafiltration has not become more general is that its byproduct, permeate, is difficult to utilize. The permeate contains the components which have gone through the ultrafiltration membrane, such as lactose, salts, and low molecular weight nitrogenous compounds. Another problem with ultrafiltration is that it is very difficult as well as expensive to obtain a high protein content (over 80 per cent of the dry substance).
Unexpectedly, it has now been found that the chromatographic separation makes it possible to fraction milk in such a manner that lactose is separated as a pure fraction while the salts remain in the protein fraction or in the protein/fat fraction. In this way a fraction nearly free from lactose and having a high protein content is obtained; on the other hand, a pure lactose solution much easier to utilize is obtained in place of the permeate. If the salts in the protein fraction are disadvantageous in view of the intended use, the protein fraction can be concentrated by ultrafiltration in place of evaporation, so that the salts are removed together with water.
Chromatographic separation by means of a cation exchange resin is a process known per se and it is an industrially applied process e.g. for the separation of saccharose from molasses and for the separation of fructose from a mixture of glucose and fructose. U.S. Pat. No. 3,969,337 describes the chromatographic fractionation of whey by means of a cation exchange resin. However, the treatment of milk includes many problems different from those connected with the treatment of whey; e.g. the susceptibility of casein to precipitate, the preservation of the micellic structure of casein, the behaviour of fat, and the extremely high hygiene requirements. Therefore, this per se known process for the separation of whey cannot be applied in the treatment of milk.